Hyperoxic lung injury is associated with widespread epithelial and endothelial injury and cell death together with airway inflammation, edema and hemorrhage. Using an induciblelung-specific transgenic system, we have shown that keratinocyte growth factor (KGF) has a profound protective effect on the lung epithelium and activates the pro-survival Akt pathway both in vivoand in vitro. We have identified intracellular molecules such as PAK4 and p90RSK that interact with the KGF receptor (KGFR)and induce pro-survivalmechanisms in lung epithelial cells. We have also found that PAK4 interacts with Raf-1 in mammaliancells. Raf-1 has been recently shown to play a critical role in cell survival. We have identified an additional property of KGF, which is blockade of neutrophil transmigration into the alveolar space, another deleterious event during oxidative injury. In related studies, we have found that the soluble form of the receptor for advanced glycation end products (sRAGE) blocks neutrophil infiltration into the lungduring hyperoxic conditions. These observations lead us to hypothesize that KGF and sRAGE inhibit oxidative lung injury through effects on cell survival and anti-inflammatory mechanisms. To test this hypothesis we will: Aim I. Determine the functional importance of the signaling network induced by activated KGFR involving RSK, PAK4 and Raf-1 in epithelial cell responses to hyperoxia. a) Mouse lung epithelial (MLE-12) cells will be subjected to hyperoxia in the presence or absence of KGF and dominant-negative(DN) mutants forKGFR-interacting proteins. Effects on a) subcellular distribution and modificationof pro- and anti-apoptotic proteins and on b) Akt and BAD phosphorylation will be followed. Aim II. Investigate the role of KGFR-interacting molecules in Akt and BADphosphorylation nad epithelial protection in vivo, a) Mice with deletions in c-Raf-1 or PAK4 in a lung epithelial cell-specific fashion in teh context of inducible KGF transgenic mice will be generated and will be subjected to hyperoxic injury. End-points will include epithelial protection and Akt and BAD phosphorylation. Aim III. Investigate the mechanismby which KGF inhibitstransepithelial neutrophil migration and study effects of KGF+sRAGE on protection from oxidativeinjury. Effects on neutrophil infiltration, chemokine secretion, matrix metalloproteinase activity, syndecan shedding, survival and edema will be followed. Aim IV. Investigate the effect of KGF on cell survival and neutrophil transmigration using a human lung epithelial cell line and primary human alveolar epithelial cells. The epithelial protective effects of KGFand inhibition of transepithelial neutrophil migration will be studied using the human lung epithelial cell line Calu-3 and primary human lung alveolar epithelial cells that can form tight junctions in vitro. Effects on hyperoxia-induced cell death and transepithelial neutrophil migration will be followed. Collectively, these studies will address the mechanisms by which KGF induces anti-apoptotic and anti-inflammatory effects.